The present invention relates generally to the bonding together of two similarly shaped portions of thermoplastic articles and more particularly involves friction welding of upper and lower container sections to provide a single hermetically welded container.
The prior art discloses a method of welding container sections together to form a single container, which method is directed to cylindrically shaped thermoplastic containers which are rotated at high speeds against each other to generate by friction the heat necessary to bond the two sections together. This prior art method is commonly referred to as spin-welding and is disclosed in such patents as U.S. Pat. No. 3,297,504, U.S. Pat. Reissue No. 29,448, and U.S. Pat. No. 3,499,068.
While the prior art method of spin-welding is advantageous over such methods as chemical bonding, cementing, and thermal bonding by means such as laser, electon beam, radio wave, and electrical means, it offers an disadvantage in that it is restricted to 20 cylindrical joints. Obviously two non-cylindrical container sections could not be successfully spin-welded because of their lack of surfaces which would maintain contact during relative rotary motion between them.
The present invention overcomes the disadvantage of rotary spin-welding by providing methods and apparatus for friction welding thermoplastic containers having non-cylindrical joinder sections as well as being applicable also to cylindrical sections. The present invention utilizes oscillatory motion, rather than rotary motion, between the two sections to be joined to provide the friction for generating the heat of bonding between the two sections.